1. Field of the Invention
This invention relates to a medicine ejection device such as an inhaler, which ejects medicines to be administered to users.
2. Related Background Art
In medicine inhalers which allow users to inhale and take medicines, treatment for users is being realized in which information databases such as electronic medical records can be utilized. Such medicine inhalers are portable terminals having in combination i) a memory means which stores information concerned with each individual user, inclusive of information on user's medical records and prescription and ii) a medicine ejection device which ejects a medicine to allow users to inhale it. They also have an ejection control means which controls the medicine ejection device in accordance with inspiration profiles of users to eject the medicine so that the users can inhale the medicine in conformity with prescription information.
In the medicine inhalers described above, a method is employed in which proper liquid droplets are ejected in a predetermined number from an ejection head (through an ejection orifice) by a system in which a liquid is ejected by producing air bubbles with a heater in the open air, i.e., air streams, to be inhaled by a user through a suction port, or a system in which a liquid is ejected by the aid of mechanical energy of a piezoelectric element.
The above conventional medicine ejection device has a problem in that the quantity of a medicine capable of being inhaled may greatly change depending on open-air environmental conditions (such as temperature, humidity and atmospheric pressure) during use of the device and on the condition of the medicine.
First, in the case of a liquid medicine, viscosity increases as the temperature of the liquid drops, and hence the volume of ejection liquid droplets tends to decrease. In particular, in the system in which the liquid is ejected by producing air bubbles with a heater, if the liquid comes to have a low temperature, thus has a high viscosity, the volume of bubbles to be produced may become small or it becomes difficult to generate bubbles. This brings about a decrease in the total amount of liquid droplets to be ejected from an ejection head, even if electric pulses are repeatedly supplied for a certain time to an electrothermal conversion element serving as a heater. As a result, the user may inhale the medicine in a smaller quantity.
If the open air comes to have a low temperature, it inevitably affects the medicine temperature. Also, as a factor other than that, it takes a time to raise the temperature of an ejection head at the initial stage of an ejection operating period of the ejection head, and hence the head comes to have poor ejection performance especially at the initial stage of the ejection operating period, resulting in a decrease in the total amount of liquid droplets to be ejected.
Depending on the humidity of the air to be sucked, the diameters of liquid droplets are changed after they have been ejected because the liquid droplets ejected from an ejection head are very small. Commonly, in order to enable intracorporeal absorption through lung alveoli, it is physiologically desirable that the liquid droplets have a diameter of about 3 μm. For example, where the medicine is ejected setting the ejection head to have a nozzle diameter of 3 μm, many liquid droplets can maintain a droplet diameter of 3 μm as long as the air is kept at a humidity as high as about 90%. However, the medicine may become deposited on the target administration portion in a smaller quantity because liquid droplets increase which come to have a smaller diameter with a decrease in humidity. In this connection, if the liquid droplets come to have too small a diameter, they are inevitably extracorporeally discharged with the user's exhaled air. As a result, the user can not inhale the medicine in a desired quantity.
The medicine comes to have a lower boiling point with a decrease in atmospheric pressure. Hence, the quantity of the medicine to be ejected tends to increase.
It is essential that the medicine be refrigerated so as not to lose its efficacy. In some cases, it is desirable that the medicine is inhaled immediately after it has been taken out of a refrigerator. For example, there may be even a case in which, while the open-air temperature at the time of inhalation is 25° C., the medicine temperature is 5° C. When the medicine inhaler is carried outdoors, there may also be a case in which the medicine is kept at a temperature close to body temperature (e.g., when carried on the body) and the inhaler is in a cold environment of about 10° C. In such a cold environment, the medicine temperature may be higher than the open-air temperature. Thus, there are circumstances where use conditions are so varied that it is difficult to make the dose of medicine constant.